Puncture resistant heat shrinkable film containing narrow molecular weight ethylene alpha olefin

Abstract

A biaxially stretched film with very high heat shrink and puncture resistance properties, formed of an ethylene alpha olefin copolymer having a density between about 0.88-0.905 g/m3, a low melt index not exceeding about 1.5 g/min, a Mw/Mn not exceeding about 3, and having a melting point below about 102 DEG C.

What is claimed is: 
     
       1. A heat shrinkable, puncture resistant biaxially stretched thermoplastic film suitable for use in fabricating bags for packaging food articles comprising a polyethylene which is a linear copolymer of ethylene and an alpha olefin containing from 4 to 8 carbon atoms, having a density between about 0.88 and about 0.905 g/cm 3 , a melt index not exceeding about 1.5 g/10 min, a molecular weight/size distribution ratio Mw/Mn not exceeding about 3, a melting point not exceeding about 102° C., a Young's Modulus not exceeding about 850 kg/cm 2 , and wherein said film shrinks at least about 45 percent at a temperature of about 90° C. in at least one of the machine and transverse directions. 
     
     
       2. A film according to claim 1 wherein said film is a monolayer film. 
     
     
       3. A film according to claim 1 wherein said film is a multilayer film and said linear copolymer comprises at least one layer of said film. 
     
     
       4. A film according to claim 1 wherein said film is a multilayer film including an oxygen barrier core layer comprising an oxygen barrier material with at least one other layer on each side thereof, and said linear copolymer comprises at least one of said other layers. 
     
     
       5. A film according to claim 4 wherein the oxygen barrier-core layer is a copolymer of vinylidene chloride. 
     
     
       6. A film according to claim 5 wherein the oxygen barrier-core layer is vinylidene chloride-vinyl chloride copolymer. 
     
     
       7. A film according to claim 5 wherein the oxygen barrier-core layer is vinylidene chloride-methyl acrylate. 
     
     
       8. A film according to claim 4 wherein the oxygen barrier-core layer is hydrolyzed ethylene vinyl acetate. 
     
     
       9. A film according to claim 1 comprising a blend of said linear copolymer and at least one other thermoplastic polymer. 
     
     
       10. A film according to claim 9 wherein said other thermoplastic polymer is another ethylene alpha olefin copolymer. 
     
     
       11. A film according to claim 10 wherein said another ethylene alpha olefin copolymer is a metallocene single site catalyzed copolymer. 
     
     
       12. A film according to claim 11 wherein said metallocene single site catalyzed copolymer is a linear copolymer of ethylene and an alpha olefin containing from 4 to 8 carbon atoms having a density between about 0.88 and about 0.905 g/cm 3 , a melt index not exceeding about 1.5 g/10 min, a molecular weight/size distribution ratio Mw/Mn not exceeding about 3, a melting point not exceeding about 100° C., and a Young's Modulus not exceeding about 850 kg/cm 2 . 
     
     
       13. A film according to claim 9 wherein said other thermoplastic polymer is ethylene vinyl acetate. 
     
     
       14. A film according to claim 10 wherein said blend, in addition to said linear copolymer and said another ethylene alpha olefin copolymer, comprises ethylene vinyl acetate. 
     
     
       15. A film according to claim 1 wherein said linear copolymer has a Vicat softening point not exceeding about 70° C. 
     
     
       16. A film according to claim 1 wherein said linear copolymer is a butene copolymer having density of about 0.88 g/cm 3 , melt index of about 0.5 g/10 min, an Mw value of about 190,000, an Mn value of about 92,600, a melting point of about 67° C., a Young's Modulus of about 400 kg/cm 2 , a dynamic puncture value of about 11.5 cmkg/mil, and a Vicat softening point of about 62° C. 
     
     
       17. A film according to claim 1 wherein said linear copolymer is a butene-hexene terpolymer having density of about 0.900 g/cm 3 , a melt index of about 1.2 g/10min, an Mw value of about 92,000, and Mn value of about 50,000, a melting point of about 94° C., a Young's Modulus of about 773 kg/cm 2 , and a Vicat softening point of between about 75° C. to about 83° C. 
     
     
       18. A film according to claim 11, wherein said metallocene single site catalyzed copolymer is a butene-hexene terpolymer having a density of about 0.900 g/cm 3 , a melt index of about 1.2 g/10 min, an Mw value of about 92,000, an Mn value of about 50,000, a melting point of about 94° C., a Youngs Modulus of about 773 kg/cm 2 , and a Vicat softening point between about 75° C. to about 83° C. 
     
     
       19. A film according to claim 1 which is crosslinked. 
     
     
       20. A film according to claim 1 which is crosslinked by irradiation. 
     
     
       21. A film according to claim 1 which shrinks at least about 55 percent in both the machine and traverse directions at 90° C. 
     
     
       22. A film according to claim 16 comprising three layers including an oxygen barrier-core layer of a vinylidene chloride-methyl acrylate copolymer and an outer layer on each side of said barrier-core layer, each of said outer layers comprising a blend of between about 65 and about 75 wt % of said linear copolymer and between about 20 and about 30 wt % ethylene vinyl acetate, and said film being crosslinked by irradiation and shrinks at least about 55 percent in both the machine and transverse directions at 90° C. 
     
     
       23. A film according to claim 2 having dynamic puncture strength of at least about 10 cmkg/mil. 
     
     
       24. A film according to claim 22 having dynamic puncture strength of at least about 3 cmkg/mil. 
     
     
       25. A film according to claim 14 wherein said linear copolymer comprises between about 30 and about 40 wt. % of said blend, said ethylene vinyl acetate comprises between about 20 and about 30 wt. % of said blend and said another ethylene alpha olefin copolymer comprises between about 30 and about 40 wt. % of said blend. 
     
     
       26. A film according to claim 12, wherein said blend, in addition to said linear copolymer and said metallocene single site catalyzed copolymer, comprises ethylene vinyl acetate. 
     
     
       27. A film according to claim 26, wherein said linear copolymer comprises between about 30 and about 40wt % of said blend, said ethylene vinyl acetate comprises between about 20 and about 30 wt. % of said blend and said metallocene single site catalyzed copolymer comprises between about 30 and about 40 wt. % of said blend.